The present invention is related to apparatus of the type providing a two-state display under the control of electromagnetic means and includes an improved switching arrangement. The display is provided by an indicator flag carried by a movable assembly mounted for rotation on a supporting structure. The indicator flag is positioned to provide a visual indication of a condition being monitored. The switching arrangement including a pair of switches is controlled by the movable assembly in a manner that respective switches are actuated to an open state from a normally closed state in substantial coincidence with a change of the visual indication. The switches may control a host of functions such as triggering a clock pulse of a logic circuit of associated equipment or they may switch the electromagnetic means so that drive energy is required only during transition of the indicator flag, among others.
Apparatus of this general type are known in the prior art. Such apparatus generally have been found to employ a member or indicator flag having discernible indicia or other discernible markings thereon such that energization of an electromagnetic assembly which may result from a change in a monitored condition causes the member to move from a first limit position to a second limit position or vice versa.
The prior art typically includes apparatus having members generally as described whereby a first display may be presented through movement of the member to a first position and a second display may be presented through movement of the member from the first to a second position. The display is adapted to be clearly visible in ambient light without the use of an illuminating source. The members, further, have been associated with means providing a self detenting or latching function in each position and there has been provision of internal switching for various reasons. The prior art apparatus generally has been of the type used to monitor electrical conditions such as the presence or absence of electrical signals in a host of environments which may require operation under conditions of shock and vibration requiring high stability, under conditions likely that there will be an ingress of dust, moisture, etc. into the confines of a housing requiring an hermetic sealing to protect the internal workings, to name to few. Also, the prior art apparatus generally are of the type which are small in size, operable under low power conditions and capable of rapid response.
A particular example of an apparatus of this type, one which substantially satisfies the above requirements, is disclosed in U.S. Pat. No. 3,573,812 to G. E. Pihl. Upon reference to the Pihl patent one may obtain insight as to the aspects of Pihl's invention and those to which his particular design of apparatus was directed. While the Pihl apparatus for the most part successfully overcame certain problems in the prior art as of the time of Pihl's invention which has been rather favorably received, the Pihl apparatus has been found not totally acceptable for reasons of complexity of structure and the costs of fabrication as well as, more importantly, problems relating to switch operation and design.